Method for producing anisoptropic bulk materials

ABSTRACT

A method is disclosed for manufacturing an anisotropic material comprising providing a viscoplastic material having a yield stress, and a plurality of magnetic particles disposed therein, and then subjecting the viscoplastic material to a magnetic field for a time sufficient to at least partially align at least a portion of the magnetic particles to at least one of a predetermined position or orientation. Also disclosed is an article having anisotropic properties comprising a viscoplastic material, and a plurality of magnetic particles distributed therein and at least partially aligned to a predetermined orientation. An article having anisotropic properties, comprising a fixed viscoplastic material, and a plurality of magnetic particles distributed and at least partially anisotropically aligned in the fixed viscoplastic material is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/804,848 filed on May 21, 2007, the content of which is relied uponand incorporated herein by reference in its entirety, and the benefit ofpriority under 35 U.S.C. §120 is hereby claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to anisotropic materials and specificallyto ceramic articles having anisotropic properties.

2. Technical Background

Magnetic particles can be oriented and aligned under the influence of amagnetic field. In certain applications, such as ferrofluids, asuspension of magnetic particles can be oriented and/or aligned in amagnetic field, but the induced order dissipates after removal of themagnetic field due to competing forces, such as gravity and Brownianmotion.

Ceramic articles can be manufactured in varying shapes and forms forapplications, such as particulate filters. In such applications, ceramicarticles can be formed with pores in the ceramic matrix to enhance thethermal conductivity, and thus, long term stability of the device. Suchceramic articles having controlled pore structures are difficult tomanufacture with current technologies.

There is a need to address the aforementioned problems and othershortcomings associated with anisotropic materials, such as, ceramicarticles. These needs and other needs are satisfied by the methods ofthe present invention.

SUMMARY OF THE INVENTION

The present invention relates to anisotropic materials and specificallyto ceramic articles having anisotropic properties. The present inventionaddresses at least a portion of the problems described above through theuse of a novel method for preparing anisotropic materials.

In a first aspect, the present invention provides a method formanufacturing an anisotropic material comprising providing aviscoplastic material having a yield stress, and a plurality of magneticparticles disposed therein; and then subjecting the viscoplasticmaterial to a magnetic field for a time sufficient to at least partiallyalign at least a portion of the magnetic particles to at least one of apredetermined position or orientation.

In a second aspect, the present invention provides an anisotropicmaterial made by the method described above.

In another aspect, the present invention provides an article havinganisotropic properties comprising a viscoplastic material and aplurality of magnetic particles distributed therein and at leastpartially aligned to at least one of a predetermined position ororientation.

In yet another aspect, the present invention provides an article havinganisotropic properties comprising a fixed viscoplastic material and aplurality of magnetic particles distributed and at least partiallyaligned to at least one of a predetermined position or orientation.

Additional aspects and advantages of the invention will be set forth, inpart, in the detailed description, figures, and any claims which follow,and in part will be derived from the detailed description or can belearned by practice of the invention. The advantages described belowwill be realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims. It is to be understoodthat both the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the invention as disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate certain aspects of the presentinvention and together with the description, serve to explain, withoutlimitation, the principles of the invention. Like numbers represent thesame elements throughout the figures.

FIG. 1 is a schematic illustrating the orientation and alignment ofnon-spherical (prolate) magnetic particles upon exposure to a magneticfield.

FIG. 2 is a schematic illustrating the orientation and alignment ofspherical magnetic particles upon exposure to a magnetic field.

FIG. 3 is a schematic illustrating the orientation and alignment ofcoated spherical magnetic particles upon exposure to a magnetic field.

FIG. 4 is a scanning electron micrograph illustrating the orientationand alignment of iron particles having a 7 μm average particle diameterin a mullite article, in accordance with various aspects of the presentinvention.

FIG. 5 is a scanning electron micrograph illustrating the orientationand alignment of iron particles having a 70 μm average particle diameterin a mullite article, in accordance with various aspects of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be understood more readily by reference to thefollowing detailed description, drawings, examples, and claims, andtheir previous and following description. However, before the presentcompositions, articles, devices, and methods are disclosed anddescribed, it is to be understood that this invention is not limited tothe specific compositions, articles, devices, and methods disclosedunless otherwise specified, as such can, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to be limiting.

The following description of the invention is provided as an enablingteaching of the invention in its currently known embodiments. To thisend, those skilled in the relevant art will recognize and appreciatethat many changes can be made to the various aspects of the inventiondescribed herein, while still obtaining the beneficial results of thepresent invention. It will also be apparent that some of the desiredbenefits of the present invention can be obtained by selecting some ofthe features of the present invention without utilizing other features.Accordingly, those who work in the art will recognize that manymodifications and adaptations to the present invention are possible andcan even be desirable in certain circumstances and are a part of thepresent invention. Thus, the following description is provided asillustrative of the principles of the present invention and not inlimitation thereof.

Disclosed are materials, compounds, compositions, and components thatcan be used for, can be used in conjunction with, can be used inpreparation for, or are products of the disclosed method andcompositions. These and other materials are disclosed herein, and it isunderstood that when combinations, subsets, interactions, groups, etc.of these materials are disclosed that while specific reference of eachvarious individual and collective combinations and permutation of thesecompounds may not be explicitly disclosed, each is specificallycontemplated and described herein. Thus, if a class of substituents A,B, and C are disclosed as well as a class of substituents D, E, and Fand an example of a combination embodiment, A-D is disclosed, then eachis individually and collectively contemplated. Thus, in this example,each of the combinations A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F arespecifically contemplated and should be considered disclosed fromdisclosure of A, B, and C; D, E, and F; and the example combination A-D.Likewise, any subset or combination of these is also specificallycontemplated and disclosed. Thus, for example, the sub-group of A-E,B-F, and C-E are specifically contemplated and should be considereddisclosed from disclosure of A, B, and C; D, E, and F; and the examplecombination A-D. This concept applies to all aspects of this disclosureincluding, but not limited to any components of the compositions andsteps in methods of making and using the disclosed compositions. Thus,if there are a variety of additional steps that can be performed it isunderstood that each of these additional steps can be performed with anyspecific embodiment or combination of embodiments of the disclosedmethods, and that each such combination is specifically contemplated andshould be considered disclosed.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a “component” includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not. For example, the phrase “optionally substituted component”means that the component can or can not be substituted and that thedescription includes both unsubstituted and substituted aspects of theinvention.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another aspect includes from the one particular value and/orto the other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

As used herein, a “wt. %” or “weight percent” or “percent by weight” ofa component, unless specifically stated to the contrary, refers to theratio of the weight of the component to the total weight of thecomposition in which the component is included, expressed as apercentage.

As used herein, a “vol. %” or “volume percent” or “percent by volume” ofa component, unless specifically stated to the contrary, refers to theratio of the volume of the component to the total volume of thecomposition in which the component is included, expressed as apercentage.

The following US patent describes various compositions and methods formaking a ceramic body, such as, for example, a honeycombed monolithicfired ceramic, and is hereby incorporated by reference in its entiretyand for the specific purpose of disclosing materials and methodsrelating to the formation of such a ceramic body: U.S. Pat. No.3,885,977.

As briefly introduced above, the present invention provides a method formanufacturing an anisotropic material through the use of a viscoplasticmaterial and a plurality of magnetic particles disposed therein. Ananisotropic material formed by the methods of the present invention canhave specifically tailored properties, such as, for example, thermalconductivity, electrical conductivity, and/or magnetic permeability. Ananisotropic material formed by the methods of the present invention canalso have a specifically tailored physical structure, such as, forexample, a structured pattern of pores.

Alignment of Magnetic Particles

It is generally known that magnetic particles can be aligned along thefield lines of a magnetic field. Particles can align to a particularorientation due to the torque (T) acting on a magnetic particle. Thetorque can be expressed by the equation T=M×H, where M represents thevector of magnetic moment of the magnetic particle and H represents thevector of intensity or strength of the magnetic field. Similar to theorientation of a compass arrow in the Earth's magnetic field, the torqueon a magnetic particle can align the particle in such a way that themagnetic moment is parallel to the magnetic field.

In addition, a magnetic field can exert a force on a magnetic particle.The perturbation of a magnetic field by individual particles can resultin a force that can attract magnetic particles together so that theyform lines or bridges in, for example, a head-to-tail alignment. Inconventional suspensions, such as, for example, ferrofluids, magneticparticles can align in the presence of a magnetic field. In theseconventional systems, the alignment and/or order of magnetic particleswill diminish after removal of the magnetic field by, for example,Brownian motion of the particles.

The present invention provides a method to induce order and/or alignmentof magnetic particles in a material wherein the order can be maintainedafter removal of the magnetic field, and even when the material isfurther heated and processed in one or more down-stream processingsteps.

Viscoplastic Material

Viscoplastic materials are one of several types of non-Newtonianliquids. Viscoplastic materials and other non-Newtonian fluids areclassified as such because they do not conform to Stokes' law ofviscosity. Viscoplastic materials have a threshold yield stress and whenthey are exposed to a shear stress less than the threshold yield stressat a given temperature or temperature range, the material behaves like asolid, showing little or no deformation. When exposed to a shear stressgreater than the threshold yield stress, the material can flow like, forexample, a viscous liquid. As a result, viscoplastic materials arefrequently referred to as “yield stress” fluids and the termsviscoplastic fluid, viscoplastic material, and yield stress fluid areall intended to refer to a viscoplastic material as described herein.Viscoplastic behavior is often associated with highly aggregatedsuspensions, such as, for example, mud, lava, paints, toothpaste,drilling fluids, ketchup, and chocolate.

The viscoplastic material of the present invention can be anyviscoplastic material or any material exhibiting viscoplastic propertiesthat is suitable for use in preparing an anisotropic article. In variousaspects, the viscoplastic material can comprise a glass material, aceramic material, a precursor material (such as, for example, one ormore raw reactants that can react to form a ceramic material, or one ormore glass material that can be transformed into a glass-ceramicmaterial upon heating), a mineral, a polymeric material or monomer(s)thereof, or a combination thereof. In one aspect, the viscoplasticmaterial comprises a ceramic material (e.g., a powdered ceramicmaterial). In another aspect, the viscoplastic material comprises amixture of ceramic materials. In another aspect, the viscoplasticmaterial comprises a mixture of ceramic materials and/or precursormaterials thereof. In a specific aspect, the viscoplastic materialcomprises an aluminum silicate, such as mullite.

A viscoplastic material can be provided in any form suitable for formingan anisotropic material. The viscoplastic material can be provided inthe form of, for example, a slurry, a paste, or a liquid, provided thatthe material exhibits viscoplastic behavior when exposed to a magneticfield. In one aspect, the viscoplastic material is provided as a slurry.In a batch stage, a viscoplastic material can exhibit a semi-solidviscoplastic property, such as, for example, when one or more powderedceramic materials are mixed with water to form a semi-solid slurry. Theviscoplastic material can be provided in the form of or substantially inthe form of the article to be produced or can be formed into a desiredshape prior to, simultaneous with, or subsequent to exposure to amagnetic field. In one aspect, the viscoplastic material is provided inthe form of a bulk article having a thickness of at least 1 mm.

The yield stress of a ceramic viscoplastic material can vary, dependingupon, for example, the water content of a slurry comprising the one ormore ceramic materials. In one aspect, the yield stress of a ceramicviscoplastic material is maintained at the same or approximately thesame value throughout the manufacturing and/or processing steps, such asfor example, mixing, extrusion, forming, and/or aligning.

The viscoplastic material can optionally be formed into a desired shapeprior to, during, or subsequent to exposure to a magnetic field. In oneaspect, the viscoplastic material is formed by, for example, anextrusion process, into a complex geometric pattern such as honeycombpattern. In a specific aspect, the viscoplastic material comprises atleast one ceramic material and is formed into a honeycomb structuredgreen body prior to exposure to a magnetic field. Such a forming stepcan result in a homogeneous distribution of magnetic particles withinthe formed green body. In another aspect, the forming process can resultin a green body having a specific desired distribution of magneticparticles, such as, for example, within the walls of a honeycombpattern.

As described above, the viscoplastic material can exhibit a desirableyield stress at a specific temperature, such as, for example, at theprocessing temperature or temperature range of interest. The yieldstress of the viscoplastic material should be sufficiently low to allowmagnetic particles disposed therein to move and at least partially alignupon exposure to a magnetic field, but should also be sufficiently highto prevent particle patterns, once formed, from breaking, upon removalof the magnetic field due to, inter alia, Brownian motion, gravitationalforce, the magnetic field of the earth, and even vibrations that can beexperienced during shipping of such material with the particlesmagnetically aligned. The yield stress of a particular viscoplasticmaterial can vary with temperature. Thus, a particular viscoplasticmaterial can be selected for use at a given temperature or range oftemperatures. Similarly, the temperature of the viscoplastic materialcan be varied and/or controlled during the exposure and optional fixingsteps to provide a specific yield stress.

In one aspect, the viscoplastic material can comprise a mixture ofmaterials, such as, for example, those described in U.S. Pat. No.3,885,977, which is incorporated by reference. In various aspects, theviscoplastic material can comprise clay, such as, for example, adelaminated kaolin clay, talc, silica, alumina, aluminum hydroxide, amagnesia-yielding chemical, or a combination thereof. In one specificaspect, the viscoplastic material comprises from about 46.6 wt. % toabout 53.0 wt. % silica, from about 33.0 wt. % to about 41.0 wt. %alumina, and from about 11.5 wt. % to about 16.5 wt. % magnesia. Inanother specific aspect, the viscoplastic material comprises about 69.2wt. % Mulcoa (available from C-E Minerals, King of Prussia, Pa., USA),about 7.7 wt. % Bentolite clay (available from Southern Clay Products,Inc., Gonzales, Tex., USA), about 5.4 wt. % of binder and/or organicmaterial, such as, for example, Methocel (available from Dow ChemicalCompany, Midland, Mich., USA), and about 17.7 wt. % water. As describedabove, the specific components and concentrations thereof can vary andthe recited examples are not intended to be limiting.

The viscoplastic material can optionally comprise additives to controland/or adjust various physical, chemical, and/or electrical propertiesof the material. Such optional additives can comprise, for example, asolvent, processing aid, rheological aid, sintering aid, or acombination thereof. In one aspect, the viscoplastic material compriseswater. In another aspect, the viscoplastic material comprises asintering aid, such as, for example, a transition metal oxide.

The viscoplastic material of the present invention can optionally becapable of being fixed. As used herein, a viscoplastic material that hasbeen fixed either no longer exhibits viscoplastic properties or has ayield stress sufficiently high as to prevent a magnetic particledisposed therein from moving by, for example, Brownian motion, or underthe force of an applied magnetic field. A viscoplastic material that iscapable of being fixed can be fixed by any suitable method, such as, forexample, cooling, curing, ceramization, cross-linking, gelling,irradiating, drying, heating, sintering, or firing.

Viscoplastic materials and optional additive materials are commerciallyavailable and one of skill in the art could readily select anappropriate viscoplastic material and optional additive suitable for usein the present invention.

Magnetic Particles

The magnetic particles of the present invention can comprise anyparticles suitable for use in a viscoplastic material and that can be atleast partially aligned and/or oriented upon exposure to a magneticfield. The specific magnetic properties, such as, for example, magneticmoment, of a magnetic particle, can vary, provided that at least aportion of the magnetic particles can be moved and/or at least partiallyaligned upon exposure to a magnetic field. The selection of a particularmagnetic particle can vary depending upon the yield stress of theviscoplastic material and/or the strength of the magnetic field used tomove and/or at least partially align a portion of the magneticparticles.

The composition of a magnetic particle can be any such compositionsuitable for use in a viscoplastic material that is capable of movingand/or at least partially aligning upon exposure to a magnetic field.The magnetic particles can, in one aspect, be ferromagnetic. In variousspecific aspects, the magnetic particles can comprise iron, cobalt,nickel, and/or an alloy, oxide, or combination thereof. In one aspect, amagnetic particle has magnetic properties different from orsubstantially different from the viscoplastic material. If aviscoplastic material, such as, for example, a ceramic materialcomprising alumina, titania, zinc oxide, or a combination thereof,exhibits magnetic properties and/or can be oriented upon exposure to amagnetic field, the magnetic particles, in various aspects, can beselected such that they have different or substantially differentmagnetic properties and can be at least partially oriented and/oraligned separately from the viscoplastic material. The composition ofany one or more magnetic particles can vary and it is not required thatall magnetic particles comprise the same composition.

The size and geometry of a magnetic particle can vary and the presentinvention is not intended to be limited to any particular size and/orshape. The present invention comprises a plurality of magnetic particlesand each individual magnetic particle or group of magnetic particles canhave either the same and/or a different size and geometry than othermagnetic particles. It should be understood that particle sizes ofmagnetic particles can be distributional properties. Thus, a particularsize can refer to an average particle diameter and the distribution ofindividual particle sizes can vary.

The magnetic particles of the present invention can have an averagediameter of from about 0.01 μm to about 1,000 μm, for example, 0.01,0.05, 0.1, 0.5, 1, 3, 5, 7, 10, 20, 40, 60, 70, 100, 200, 400, 500, 700,or 1,000 μm. In one aspect, the magnetic particles have an averagediameter of about 7 μm. In another aspect, the magnetic particles havean average diameter of about 70 μm. In yet another aspect, the magneticparticles can comprise a multi-modal distribution of particle sizes,such as, for example, a first mode having an average diameter of about 7μm and a second mode having an average diameter of about 70 μm.

The geometry of a magnetic particle can also vary, provided that themagnetic particle is capable of moving and/or at least partiallyorienting and/or aligning upon exposure to a magnetic field. A magneticparticle can, in one aspect, have an elongated shape, such as, forexample, prolate. Magnetic particles having an elongated shape can, inone aspect, align in a pattern, such as, for example, a line along theaxis of the elongated particles, as illustrated in FIG. 1. Such analignment of elongated magnetic particles can be useful, for example, inthe formation of elongated pores in a fired ceramic article. The aspectratio of an elongated magnetic particle can vary and the presentinvention is not intended to be limited to a magnetic particle having aparticular aspect ratio. In another aspect, a magnetic particle can havea spherical shape, as illustrated in FIG. 2. In another aspect, amagnetic particle can have a flake morphology. In yet another aspect,the plurality of magnetic particles comprises a mixture of magneticparticles having various shapes, such as, for example, elongatedparticles and spherical particles.

The surface of a magnetic particle can have any morphology and/orsurface property suitable for use in the provided viscoplastic material.In one aspect, at least a portion of the magnetic particles have a roughand/or jagged surface. In another aspect, at least a portion of themagnetic particles have a smooth surface.

The magnetic particles of the present invention can exhibit thermaland/or electrical conductivity properties that are substantiallydifferent from the viscoplastic material and/or the solid matrix of afinished article. In one aspect, at least a portion of the plurality ofmagnetic particles have a thermal conductivity that is substantiallydifferent from that of the viscoplastic material. In another aspect, atleast a portion of the plurality of magnetic particles have anelectrical conductivity that is substantially different from that of theviscoplastic material. In another aspect, the plurality of magneticparticles have thermal and electrical conductivities that aresubstantially different from those of the viscoplastic material.

The magnetic particles of the present invention can optionally comprisea coating. A coating, if present, can cover a portion of or the entiretyof any single magnetic particle and can be uniform or can vary fromparticle to particle. In one aspect, a coating material covers a portionof each of a plurality of magnetic particles. In another aspect, acoating material covers all of the surface of each of a plurality ofmagnetic particles, as illustrated in FIG. 3. In another aspect, one ormore coating materials can be used and can vary across the surface ofany individual or group of magnetic particles. The composition andproperties of a particular coating material can vary depending on theintended application and the specific properties to be imparted toeither the magnetic particles and/or the viscoplastic material. In oneaspect, the magnetic particles comprise a coating that can reduce and/oreliminate chemical reaction between the magnetic particle and theviscoplastic material and/or an additive thereto. In another aspect, themagnetic particles comprise a coating that can reduce and/or eliminateoxidation of a magnetic particle. In yet another aspect, the magneticparticles comprise a coating that can react with a surrounding material.In yet another aspect, the magnetic particles can comprise a coatingthat can be volatilized and/or removed during a subsequent heating step.In a specific aspect, at least a portion of the magnetic particlescomprise a pore-forming material, such as, for example, a starch, thatcan be volatilized and/or combusted during a subsequent heating step,such as firing of a ceramic article. In another specific aspect, atleast a portion of the magnetic particles comprise a polymer coating.

The magnetic particles of the present invention can be added to theviscoplastic material at any level suitable for producing an articlehaving desired anisotropic properties. In various aspects, the magneticparticles can comprise from greater than 0 to about 40 volume percent,for example, about 0.1, 0.3, 0.6, 1.0, 1.3, 1.7, 2.2, 2.6, 3.2, 3.8,4.1, 4.8, 5.0, 7.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, or 40.0 volumepercent of the composition (viscoplastic material and magneticparticles). In one aspect, the volume percent of magnetic particles in acomposition is sufficiently high such that at least a portion of themagnetic particles can align in, for example, a head-to-tail fashion. Ina specific aspect, the magnetic particles are present at a sufficientlevel to allow head-to-tail contact between at least a portion of or allof the magnetic particles aligned in a particular pattern. In anotheraspect, the volume percent of magnetic particles in a composition issufficiently low such that at least a portion of the magnetic particlesare not connected and/or adjacent to other magnetic particles. Thespecific volume percent of one or more magnetic particles in acomposition can vary based on the desired properties or application of afinished article and one of skill in the art could readily select anappropriate volume percent level for a particular viscoplastic material,magnetic particle, and/or intended application.

The magnetic particles of the present invention can be combined with theviscoplastic material in any manner suitable for manufacturing ananisotropic material. The magnetic particles can be at least partiallydistributed in or on the viscoplastic material. In one aspect, themagnetic particles are distributed in the matrix of the viscoplasticmaterial. In another aspect, the magnetic particles are uniformly mixedin the viscoplastic material. In other various aspects, at least aportion of the magnetic particles are positioned in one or more discretelocations in or on the viscoplastic material, arranged in a pattern inor on the viscoplastic material, or a combination thereof. In variousaspects, separate portions of the same of different viscoplasticmaterial comprising varying volume percent levels of magnetic particlescan be combined to form a green body having a biased or preferentialdistribution of magnetic particles. Various forming techniques that canprovide non-uniform distributions of materials, such as magneticparticles, are known and one of skill in the art could readily select anappropriate forming technique to extrude and/or form a green body havingeither a uniform or non-uniform distribution of magnetic particles.

Magnetic particles and optional coating materials are commerciallyavailable and one of skill in the art could readily select anappropriate magnetic particle and optional coating material for use inthe present invention.

Exposure To Magnetic Field

The magnetic field of the present invention can be any magnetic fieldsuitable for use in moving and/or at least partially orienting and/oraligning at least a portion of the magnetic particles disposed in aviscoplastic material. Further, the magnetic field can be generated byany suitable means provided that at least a portion of the viscoplasticmaterial having a plurality of magnetic particles disposed therein iscapable of being exposed to at least a portion of the magnetic field. Inone aspect, a portion of the viscoplastic material is exposed to aportion of the magnetic field. In another aspect, all of theviscoplastic material is exposed to a portion of the magnetic field. Itis not required that either all of or a portion of a viscoplasticmaterial be positioned at any specific location within the magneticfield.

The magnetic field of the present invention should have a strengthsufficient to move and/or at least partially orient and/or align atleast a portion of the magnetic particles disposed in the viscoplasticmaterial. The magnetic field can be referred to as B (magnetic inductioncurrent) or H (magnetic field, or circumferential velocity of vortices)and can be expressed in units of Tesla (T), amperes per meter (A/m),Gauss (G), or Oersteds (O_(e)). The field strength necessary to orientand positionally align a magnetic particle in a viscoplastic materialcan be expressed by the equation

M·H>S·R·σ ₀

where M is the magnetic moment of the magnetic particle, H is the fieldstrength of the magnetic field, S is the surface area of the magneticparticle, R is the half-diameter of the magnetic particle, and σ₀represents the yield stress of the viscoplastic material. The presentinvention is directed to moving and at least partially orienting and/oraligning at least a portion of the magnetic particles disposed in aviscoplastic material. It is not necessary that all of the magneticparticles be moved and/or aligned or that any individual magneticparticle be aligned to a specific extent. Thus, it is preferred, but notnecessary that the strength of the magnetic field be sufficient toorient and positionally align almost all or all of the magneticparticles as described by the above equation. In one aspect, thestrength of the magnetic field is greater than the strength of thenatural magnetic field of the Earth.

In the present invention, the at least partially oriented and/or alignedmagnetic particles can remain oriented and/or aligned, provided that theyield stress of the viscoplastic material is sufficiently high toprevent movement, such as, for example, gravitational sedimentation, ofthe particles, even after removal of the magnetic field. The orientationand position of the at least partially oriented and/or aligned magneticparticles can remain unchanged until such time as they are exposed toanother sufficiently strong magnetic field or the viscoplastic materialflows under, for example, gravitational force.

In various aspects, the magnetic field can have a field strength of fromabout 100 to about 100,000 Gauss. In a specific aspect, the magneticfield has a strength of about 6000 G. The field strength of a magneticfield can vary, depending upon the specific magnetic particles used, thespecific viscoplastic material, and/or the degree of orientation and/oralignment desired and one of skill in the art could readily select anappropriate magnetic field strength for a specific application.

The viscoplastic material having the plurality of magnetic particlesdisposed therein can be exposed to the magnetic field for a sufficienttime to allow at least a portion of the magnetic particles to moveand/or at least partially orient and/or align. The specific time that aviscoplastic material is exposed to the magnetic field can vary,depending on the strength of the magnetic field, the yield stress andtemperature of the viscoplastic material, and the particular magneticparticles employed. In one aspect, the viscoplastic material is exposedto the magnetic field for a period of about 30 seconds. In anotheraspect, the viscoplastic material is exposed to the magnetic field for aperiod of about 10 minutes.

Upon exposure to the magnetic field, at least a portion of the pluralityof magnetic particles can move and at least partially orient and/oralign with one or more lines of the magnetic field. The magneticparticles can align to a predetermined position and/or orientation,according to the magnetic field lines, as a result of the torque exertedon the particles by the magnetic field, as illustrated by the prolate,spherical, and coated spherical magnetic particles of FIGS. 1-3.

In one aspect, the magnetic particles of the present invention can beoriented and/or positioned in a three dimensional distribution within aviscoplastic material. In a specific aspect, the magnetic particles canbe aligned at various points within a bulk viscoplastic material and thealignment is not limited to a surface portion or thin layer. Themagnetic field of the present invention can be one or more separatemagnetic fields, each having independent magnetic field lines. In oneaspect, the viscoplastic material can be exposed to a plurality ofmagnetic fields using, for example, one or more electromagnets, toprovide complicated orientation and alignment patterns of magneticparticles in a viscoplastic material.

It should be noted that, depending on the nature of the magnetic fieldand the equipment used for producing the magnetic field, the lines ofthe magnetic field may not be parallel. Magnetic particles orientedand/or positioned according to the methods of the present invention willalign according to the field lines of the magnetic field. Variousmethods exist to alter the lines of a magnetic field. In addition, aviscoplastic material can be moved within a magnetic field to alterportion of the material exposed to a particular field line. The use ofthese methods and variants of the methods described herein are intendedto be included in the present invention.

It should also be noted that, the magnetic field used for treating thematerial can vary in direction and/or strength during the process ofsubjecting the magnetic particles to the magnetic field. Such variationand/or modulation of the magnetic field can, in various aspects, resultin a desirable orientation, movement, and/or alignment of at least aportion of the magnetic particles.

In one aspect, the magnetic particles are subjected to the magneticfield after the forming the composition (i.e., viscoplastic material andmagnetic particles) into a desired shape and/or geometry. In a specificaspect, a composition comprising a viscoplastic material and a pluralityof magnetic particles can be formed into a green body honeycombstructure by, for example, an extrusion process, and subsequently besubjected to a magnetic field such that at least a portion of themagnetic particles disposed within the viscoplastic material areoriented in the cell walls of the green body honeycomb structure.Alternatively, exposure to a magnetic field and thus, orientation and/oralignment of at least a portion of the magnetic particles disposedwithin a viscoplastic material can be performed prior to a forming step.

Magnetic fields and the equipment for generating magnetic fields areknown and commercially available and one of skill in the art couldreadily select an appropriate magnetic field for a particularcombination of viscoplastic material and magnetic particles or for aspecific application.

Fixing Magnetic Particles

Once the magnetic particles are at least partially oriented and/oraligned, their orientation and position can optionally be fixed withinthe viscoplastic material. A fixing step can comprise any suitabletechnique for permanently or semi-permanently fixing the orientation andposition of the magnetic particles within the viscoplastic material. Afixing step, if performed, can vary depending on the nature of theviscoplastic material. In various aspects, the optional fixing step cancomprise cooling, curing, cross-linking, ceramizing, irradiating,drying, gelling, heating, sintering, firing, polymerizing, or acombination thereof. A fixed viscoplastic material can be referred to asa solid material and does not exhibit viscoplastic properties. In oneaspect, the viscoplastic material comprises a polymeric material thatcan be cross-linked by, for example, thermal, chemical and/or opticalmeans. In another aspect, the viscoplastic material comprises a slurrycomprising a glass material, a ceramic material, or precursor materialsthereof that can be dried, heated, and/or fired to form a refractoryceramic body. In a specific aspect, a viscoplastic material comprisingmullite, after exposure to a magnetic field, can be dried at about 75°C. for a period of about 24 hours and then be fired to a maximumtemperature of about 1,350° C. to form a refractory ceramic.

The optional fixing step of the present invention can be performedduring the subjecting step (i.e., exposure to the magnetic field) orafter the magnetic field has been removed, withdrawn, and/or diminishedto a level that is no longer capable of orienting and/or aligning themagnetic particles. In one aspect, a fixing step is performed duringexposure to the magnetic field. In another aspect, a fixing step isperformed after the magnetic field has been removed.

Optional Steps

A viscoplastic material comprising at least partially aligned and/ororiented magnetic particles can optionally be subjected to subsequenttreatment steps. In one aspect, a fixed material comprising mullite andmagnetic particles having a pore-former coating can be heated tovolatilize and/or combust the pore-forming material. Alternatively, thepore-forming material can be volatilized and/or combusted during afiring step to for a refractory ceramic. Such a treatment can result inthe formation of, for example, a plurality of parallel pores within thebody of the refractory ceramic in a pattern matching the location of theat least partially oriented and/or aligned magnetic particles. In oneaspect, this technique can be used to provide a controlled porestructure in a ceramic article. In another aspect, this technique can beused to provide an article having a low percentage of dead-end pores. Insuch an application, the alignment of magnetic particles can improve thedistribution of a pore-forming material. In certain application, suchas, for example, particulate filters, a ceramic article having a lowpercentage of dead-end pores can be advantageous by improving thethermal conductivity of the article.

The at least partially oriented and/or aligned magnetic particles canoptionally be removed from a finished article using any suitabletechnique. In one aspect, at least a portion of the magnetic particlescan be removed from a pore by, for example, an acid washing technique. Afinished article of the present invention can comprise the plurality ofmagnetic particles, a portion of the plurality of magnetic particles, orno magnetic particles, and the present invention is not intended to belimited to a specific aspect having magnetic particles remainingdisposed therein.

In another aspect, at least a portion of the plurality of magneticparticles can be fused together during, for example, a subsequentheating and/or firing step.

Although several aspects of the present invention have been illustratedin the accompanying drawings and described in the detailed description,it should be understood that the invention is not limited to the aspectsdisclosed, but is capable of numerous rearrangements, modifications andsubstitutions without departing from the spirit of the invention as setforth and defined by the following claims.

EXAMPLES

To further illustrate the principles of the present invention, thefollowing examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how thecompositions, articles, devices, and methods claimed herein are made andevaluated. They are intended to be purely exemplary of the invention andare not intended to limit the scope of what the inventors regard astheir invention. Efforts have been made to ensure accuracy with respectto numbers (e.g., amounts, temperatures, etc.); however, some errors anddeviations should be accounted for. Unless indicated otherwise,temperature is ° C. or is at ambient temperature, and pressure is at ornear atmospheric. There are numerous variations and combinations ofprocess conditions that can be used to optimize product quality andperformance. Only reasonable and routine experimentation will berequired to optimize such process conditions.

Example 1 Preparation of Mullite Articles

In a first example, two test articles were prepared by mixing mullitepowder (such as that available from C-E Minerals, King of Prussia, Pa.,USA) with iron powder. A first article was prepared by mixing a mullitepowder, an iron powder having a 7 μm average particle diameter(available from Alfa Aesar, Ward Hill, Mass., USA), and water to form acement slurry. A second article was similarly prepared by mixing amullite powder, an iron powder having a 70 μm average particle diameter(available from ESPI Metals, Ashland, Oreg., USA), and water to form acement slurry. Each slurry sample was exposed to a uniform magneticfield of 6000 Gauss for 30 seconds. After exposure, the cement sampleswere dried at 75° C. for 24 hours and subsequently fired to a maximumtemperature of 1,350° C. The volume fraction of iron particles in eachfired article did not exceed 5%. FIGS. 4 and 5 illustrate theorientation and alignment of the iron particles (light or white areas)in the mullite articles after exposure to the magnetic field. Theposition and alignment of iron particles within each sample, asillustrated in FIGS. 4 and 5, was similar and not dependent on the sizeand/or shape of the iron particles.

Throughout this application, various publications are referenced. Thedisclosures of these publications in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the compositions, articles, device, and methods describedherein.

Various modifications and variations can be made to the compositions,articles, devices, and methods described herein. Other aspects of thecompositions, articles, devices, and methods described herein will beapparent from consideration of the specification and practice of thecompositions, articles, devices, and methods disclosed herein. It isintended that the specification and examples be considered as exemplary.

1. A method for manufacturing an anisotropic material comprising a)providing a viscoplastic material having a yield stress, and a pluralityof magnetic particles disposed therein; and then b) subjecting theviscoplastic material to a magnetic field for a time sufficient to atleast partially align at least a portion of the magnetic particles to atleast one of a predetermined position or orientation, wherein themagnetic particles are suspended throughout the viscoplastic material.2. The method of claim 1, wherein a stress is created on theviscoplastic material by Brownian motion and/or gravitational movementof at least a portion of the plurality of magnetic particles, andwherein the stress is less than the yield stress of the viscoplasticmaterial.
 3. The method of claim 1, wherein the providing of step a)comprises forming the viscoplastic material into a desired shape.
 4. Themethod of claim 3, wherein the desired shape is a honeycomb structure.5. The method of claim 1, wherein at least a portion of the plurality ofmagnetic particles have a thermal conductivity and/or an electricalconductivity substantially different from the viscoplastic material. 6.The method of claim 1, wherein, after subjecting, at least a portion ofthe plurality of magnetic particles are oriented in a head-to-tailpattern.
 7. The method of claim 1, wherein at least a portion of theplurality of magnetic particles subjected to the magnetic field create astress on the viscoplastic material greater than the yield stress. 8.The method of claim 1, wherein the viscoplastic material comprises aglass material, a ceramic material, and/or a precursor or combinationthereof.
 9. The method of claim 1, wherein at least a portion of theplurality of magnetic particles are ferromagnetic.
 10. The method ofclaim 1, wherein at least a portion of the plurality of magneticparticles are at least partially distributed in at least a portion ofthe viscoplastic material.
 11. The method of claim 1, wherein at least aportion of the plurality of magnetic particles are spherical, elongated,or a combination thereof.
 12. The method of claim 1, wherein at least aportion of the plurality of magnetic particles comprise a pore-formingmaterial.
 13. The method of claim 1, further comprising fixing at leasta portion of the plurality of magnetic particles within the viscoplasticmaterial in an at least partially aligned state.
 14. The method of claim13, wherein the fixing is carried out after the magnetic field has beenremoved, withdrawn, and/or diminished to a level that is no longercapable of orienting and/or aligning the magnetic particles.
 15. Themethod of claim 13, wherein fixing comprises at least one of cooling,curing, ceramizing, cross-linking, gelling, sintering, polymerizing,irradiating, heating, or firing the viscoplastic material.
 16. Themethod of claim 13, wherein at least a portion of the plurality ofmagnetic particles comprise a pore-forming material, and furthercomprising heating the viscoplastic material, after fixing, to form aplurality of pores.
 17. The method of claim 16, wherein at least aportion of the magnetic particles, after step b), are in contact suchthat upon heating, at least a portion of the plurality of pores connectin a head-to-tail fashion to form a line.
 18. The method of claim 16,wherein at least a portion of the plurality of magnetic particles reactwith a surrounding material during the fixing step.
 19. The method ofclaim 16, wherein at least a portion of the pore-forming materialvolatilizes during the fixing step such that a void is created.
 20. Themethod of claim 16, wherein the fixing step comprises the formation of afired ceramic material from at least one precursor material thereof. 21.The method of claim 1, wherein the viscoplastic material has a thicknessof greater than about 1 mm.
 22. The method of claim 1, wherein themagnetic field comprises a plurality of magnetic fields.